In order to conserve energy in electronic circuits, particularly in battery-operated electronics, it is preferable to use bias currents which are no larger than necessary. Therefore, because the minimum required bias current tends to depend on signal amplitude, it is often desirable to use actual bias currents which are dependent on the amplitude of the signal. An additional advantage of amplitude-dependent biasing is that, if the bias current is only as large as needed, it will produce the least possible amount of noise (e.g., shot noise). These advantages have been discussed in the electronics literature with respect to at least one specific log-domain circuit. D. R. Frey and Y. P. Tsividis, xe2x80x9cSyllabically Companding Log Domain Filter Using Dynamic Biasing,xe2x80x9d Electronics Letters, vol. 33, no. 5, Aug. 28, 1997. Amplitude-dependent biasing can used in other circuits, e.g., amplifiers. However, one potential problem is that the bias can, in some cases, interact with the signal. Accordingly, there is a need for circuits in which the bias control and the signal properties are xe2x80x9corthogonalxe2x80x9dxe2x80x94i.e., do not interact with each other.
It is therefore an object of the invention to provide a circuit which can accommodate signals of various amplitudes in an energy-efficient manner.
It is a further object of the invention to provide a circuit which can accommodate signals of various amplitudes while maintaining a high signal-to-noise ratio.
It is yet another object of the invention to provide a circuit which can accommodate signals of various amplitudes while avoiding excessive interaction between the bias control and the signal.
These and other objects are accomplished by a circuit having a bias which can be adjusted according to a signal which is received, generated, or transmitted by the circuit.
In accordance with one aspect of the invention, a signal is processed using an apparatus comprising: (1) a selected one of a class-AB circuit and a class-B circuit, the selected one having at least one input and at least one bias, the at least one input being adapted to receive at least one input signal, and the selected one being configured to process the at least one input signal to thereby generate at least one output signal related to the at least one input signal by an input-output characteristic having a crossover region which exhibits distortion; and (2) an amplitude detector configured to perform the operations of: (a) receiving the at least one input signal; (b) detecting at least one amplitude of the at least one input signal, and (c) dynamically adjusting the at least one bias in accordance with the at least one amplitude, wherein the at least one bias controls a level of the at least one output signal such that the at least one output signal avoids the crossover region.
In accordance with another aspect of the invention, a signal is processed using a filter having at least one input and at least one bias, wherein the at least one input comprises: (1) a first input for receiving a first input signal; and (2) a second input for receiving a second input signal, wherein the filter is configured to perform the steps of: (a) applying a first filtering operation to the first input signal, thereby generating a first output signal which is communicated to at least one output of the filter, the first filtering operation having a first frequency characteristic in which low frequencies are suppressed, and (b) applying a second filtering operation to the second input signal, the second input signal controlling the at least one bias, the second filtering operation having a second frequency characteristic in which low frequencies are passed, and the second input signal being adjusted in accordance with an amplitude of the first input signal.
In accordance with an additional aspect of the invention, a signal is processed using a filter having at least one input and first and second biases, wherein the at least one input comprises first and second inputs, the first input being adapted to receive a first input signal and a first bias signal related to an amplitude of at least one of the first and second input signals, the first bias signal being for controlling the first bias, the second input being adapted to receive a second input signal and a second bias signal, the second bias signal being for controlling the second bias, the second bias signal being approximately equal to the first bias signal, and the filter being configured to filter a difference of first and second input signals, thereby generating a filter output signal.
In accordance with another aspect of the invention, a signal is processed using a combined filter comprising: (1) a first filter having a first filter configuration, a first bias input for receiving a first bias, a first input for receiving a first input signal, and a first output for providing a first output signal; (2) a second filter having a second filter configuration, a second bias input for receiving a second bias, a second input for receiving a second input signal, and a second output for providing a second output signal, the second filter configuration matching the first filter configuration, the first bias and the second bias being adjusted in accordance with at least one amplitude of at least one of the first input signal and the second input signal, and the first bias and the second bias being adjusted to be approximately equal; and (3) a combined filter output configured to provide a combined output signal comprising a difference of the first output signal and the second output signal.
In accordance with yet another aspect of the invention, a signal is processed using an apparatus comprising: (1) a first transistor, comprising a first signal-receiving terminal, a first current-carrying terminal adapted to be connected to a voltage source, and a second current-carrying terminal connected to the first signal-receiving terminal; (2) a second transistor, comprising: a second signal-receiving terminal connected to the first signal-receiving terminal, a third current-carrying terminal adapted to be connected to the voltage source, and a fourth current-carrying terminal; (3) a first adjustable current source in communication with the second current-carrying terminal and allowing a first bias current to flow through the second current-carrying terminal; (4) a second adjustable current source in communication with the fourth current-carrying terminal and allowing a second bias current to flow through the fourth current-carrying terminal, the second bias current being approximately equal to the first bias current, and the first and second adjustable current sources being adjusted in accordance with an amplitude of a first input signal coupled into at least one of the second current-carrying terminal and the fourth current-carrying terminal; and (5) an output connected to the fourth current-carrying terminal.
In accordance with an additional aspect of the invention, a signal is processed using an apparatus comprising: (1) a dynamically biased signal-processing circuit having an input and an output; and (2) a feedback path providing a feedback signal from the output to the input.
In accordance with a further aspect of the invention, a signal size is detected by a detector comprising: (1) a differencing block configured to perform the operations of: (a) receiving a first input signal, (b) receiving a second input signal, and (c) generating a difference signal comprising a difference of the first and second input signals; (2) an exponentiator configured to exponentiate a signal comprising the difference signal, thereby generating an exponentiated signal, wherein an output signal of the detector comprises the exponentiated signal; and (3) a filter configured to perform low-pass filtering of a signal comprising the difference signal, thereby generating a filtered signal, wherein the output signal further comprises the filtered signal, and wherein the second input signal comprises the output signal.
In accordance with yet another aspect of the invention, a signal size is detected by a detector comprising: (1) first, second, third, fourth, and fifth nodes, wherein an input signal is received by the first node; (2) a first transistor, comprising: (a) a first signal-receiving terminal connected to the second node, (b) a first current-carrying terminal connected to the third node, and (c) a second current-carrying terminal adapted to receive a first bias current; (3) a second transistor, comprising: (a) a second signal-receiving terminal connected to the fourth node, (b) a third current-carrying terminal connected to the third node, and (c) a fourth current-carrying terminal adapted to receive a second bias current, the fourth current-carrying terminal being connected to the fourth node; (4) a high-frequency shunt connected between the fourth node and a first voltage node, the first voltage node being adapted to be connected to a first voltage source; (5) a third transistor, comprising: (a) a third signal-receiving terminal connected to the fourth node, (b) a fifth current-carrying terminal connected to the fifth node, and (c) a sixth current-carrying terminal adapted to receive a third bias current; and (6) a fourth transistor, comprising: (a) a fourth signal-receiving terminal adapted to be connected to a second voltage source, (b) a seventh current-carrying terminal connected to the fifth node, and (c) an eighth current-carrying terminal connected to the first node.